The manufacture of synthetic paper making fibers, commonly referred to as fibrils, by precipitating an olefin polymer from a hydrocarbon solution is known. A number of different processes are reported for manufacturing such fibrils and fibrils are offered for commercial sale in the United States by at least two suppliers. See U.S. Pat. No. 2,988,782; U.S. Pat. No. 3,740,493; and U.S. Pat. No. 4,013,751. Although fibrils made by different processes and/or obtained from different sources are essentially indistinguishable from each other by physical examination, it has been noted that waterlaid sheets prepared from different types of fibrils differ significantly from each other in important properties. These observed differences are believed to result from small differences in fibril structure which are difficult to detect by physical observation.
U.S. Pat. No. 4,049,493 discloses that a two-step process of first refining fibrils in the presence of a water miscible solvent such as isopropanol and then further refining such fibrils in an aqueous solution of a surfactant, including polyvinyl alcohol, improves the quality of waterlaid sheets prepared from such fibrils. Both refining steps are carried out under conditions of high shear stress as developed in a Waring Blendor. Fibrils prepared by this process have excellent properties. A limitation of the process, however, is the requirement that both refining steps be carried out under conditions of high shear stress.